Design, synthesis and applications of a dual-mode peptidyl probe for sequential determination of Cu2+ and S2- in food and biological systems.

Copper ions (Cu2+) and sulfide ions (S2-) are important markers in many physiologies processes. However, its excessive emissions have caused serious harm to biological systems and ecological environment. Herein, a new dual-mode fluorescent and colorimetric peptidyl probe NGHK was developed based on 7-Nitro-2,1,3-benzoxadiazole (NBD) fluorophore coupled tripeptide backbone (Gly-His-Lys-NH2). NGHK exhibited excellent selectivity (only Cu2+), high sensitivity (LOD = 74.5 nM), rapid response (within 50 s) and wider pH range (6.0-12.0) towards Cu2+ in 10.0 mM HEPES buffer at pH 7.4, with the non-fluorescence complex (NGHK-Cu2+) formation via the 1:1 binding mode. Interestingly, NGHK-Cu2+ ensemble exhibited dual-mode responses to S2- through obvious color changes and fluorescence enhancement responses, the limit of detection (LOD) for S2- was 36.9 nM. In addition, NGHK was used for fluorescence imaging in living cells and zebrafish larvae based on the satisfactory low toxicity. For practical applications, NGHK was not only capable of monitoring Cu2+ and S2- concentrations in real food and water samples with satisfactory results, but also could conduct the analysis of the surface of actual samples. Utilizing NGHK, we also developed the portable test strips for the visual detection of Cu2+ and S2-. Simultaneously, NGHK was successfully developed as an ultrasensitive logic gate with truth table.